351w w/c-6 or 300 w/c-6

H-DFord · Post by **H-DFord** » Mon Oct 20, 2008 8:42 am

A friend found me a 351w with c-6 combo out of a 3/4 ton van. Is anyone running this combo and if so what kind of fuel mileage are you getting with it? I have also found a 300 but still hunting a c-6 to put behind it. Is anyone running this combo and tracked your fuel mileage. Both engines will have carb on them and the truck is running 325 gears in rearend. Thanks for any input, John.

craftsman · Post by **craftsman** » Tue Oct 21, 2008 7:21 am

I have a 1985 351w ho engine with c6 and 3.50 gear rear end and it sucks gas, 9 mpg.

I don't know about the 300 and c6.

SteveC · Post by **SteveC** » Tue Oct 21, 2008 7:32 am

i have a 351w with a fmx and 2.75 gears in a ltd that gets between 10-15 depending on how you drive

H-DFord · Post by **H-DFord** » Tue Oct 21, 2008 8:54 am

Thanks for your input on the 351. That kind of lines up with everything else Ive been told. I guess I should be looking at the 300 six. Guy I know got 15 with 4-spd Im just wondering how much a c-6 would hurt it. John

j41385 · Post by **j41385** » Tue Oct 21, 2008 6:11 pm

My 300 has a c6 trans, and 3.55 rear end gears. I get 17 mpg.

H-DFord · Post by **H-DFord** » Wed Oct 22, 2008 7:31 am

Thanks for your reply on the 300 c-6 combo. I'm leaning that way myself. John

willowbilly3 · Post by **willowbilly3** » Wed Oct 22, 2008 7:56 am

I wouldn't put a c6 behind a 300. The parasitic drain is huge on those big transmissions and a c4 can handle anything a 300 will dish out with about half the drag. The 17 mpg with a c6 would probably be 20 with a stick. I would even consider an AOD, except for the huge $$ they get to rebuild them.
If you use the c6, remember there is about 200-250 rpm slippage at cruise so gear accordingly.

Post by **DuckRyder** » Wed Oct 22, 2008 8:03 am

I agree withthe 300/AOD idea, I know they used some c-6 behind 300's in particular in Econolines, but a C-6 seems overkill to me... of course it would last forever...

H-DFord · Post by **H-DFord** » Wed Oct 22, 2008 8:53 am

So would the c-4 be a good choice for this or do I need to find an aod. I'm not completely up on all this, what year models would an aod be in and does it require anything extra to make it work. John

willowbilly3 · Post by **willowbilly3** » Wed Oct 22, 2008 7:58 pm

The earlier AOD was not computerized but I don't know the cut off year. I have heard the lockup convertor is the weakest point and you can use a regular one. But i also think the lockup does as much for mileage as the od gear. I'm going to say maybe 79 to 84-85 would be non computerized. The C4 is a stout little tranny and fairly simple (read less expensive to build)

H-DFord · Post by **H-DFord** » Thu Oct 23, 2008 7:07 am

Thanks for all the input here for this. I'm going to check on the 300 this weekend then ill start seeing what kind of trans I can find. So im guessing the aod would get me better mileage than a c-4? Will it be a big difference? Thanks again for everyone's input. John

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351w w/c-6 or 300 w/c-6

351w w/c-6 or 300 w/c-6

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